I. Field of the Invention
The present invention is directed to a driver circuit which produces an output voltage of 20V and higher. In particular, the present invention provides a high voltage driver circuit constructed of CMOS technology and capable of producing an output voltage swing of 20V-40V.
II. Description of the Related Art
A number of optical modulator technologies are currently being considered for fiber-to-the-home applications wherein downstream light on a fiber is modulated and the data signal is returned upstream. Such devices have also been suggested for use in linear-array formats to facilitate wavelength-division multiplexing. Other devices have been proposed for high-density two-dimensional chip-to-chip interconnect applications which require input drive signals in the range of 20V-40V for effective performance. However, typical commodity silicon VLSI technologies can only provide drive voltages of about 5V. Although conventional driver chips using special purpose technologies can provide higher voltage swings at moderate speeds of a few Mb/s, an integrated driver circuit is needed to provide a low cost, low volume, high-speed (1 Mbit/s to.gtoreq.100 Mb/s) packaged device capable of producing an output voltage range of 20V-40V.
The main deterrent in designing a high-voltage driver circuit in widely available CMOS technologies is the low breakdown voltage of the transistors. Breakdown can occur due to punch-through of electrons through the gate oxide or when two depletion regions merge to cause a short. For instance, data acquired from the MOSIS CMOS foundry has established that the minimum measured punch-through voltages of a PMOS are 8.6V, 11.0V, 11.9V and 12.5V for the 0.5 .mu.m, 0.8 .mu.m, 1.2.mu., and 2.0 .mu.m CMOS technologies, respectively. A high-voltage driver circuit must therefore provide large output swings while ensuring that the voltage between any pair of nodes is at all times below its specified breakdown voltage.